1. Field of the Invention
This invention relates to a method for producing diamonds, and more specifically, this invention relates to a method for producing nanometer-sized diamonds from carbonaceous materials by ion irradiation.
2. Background of the Invention
Nanodiamonds have various technological applications, including as fine polishing and grinding abrasives. Other possible uses for nanodiamonds include their use as powders with high thermal conductivity for use as heat sinks. Inasmuch as such media are both chemically resistant and electrically nonconducting, their suspension in advanced coolant fluids will enhance heat transport.
Nanodiamonds also can be utilized as an admixture in advanced composite materials to enhance thermal conductivity or surface hardness.
Lastly, nanodiamonds may be utilized as seed crystals for growth of larger diamonds.
The free energy difference between diamond and graphite is small. However, transformation between the two allotropes is difficult. This is because the high stability of the basal graphite planes requires the presence of catalysts, or thermodynamic conditions deep within the diamond phase region, for solid-state transformation of graphite into diamond.
A myriad of techniques exist to produce nanodiamonds. However, these processes require extreme conditions, such as high pressure, high temperature, or high irradiation fluence. For example, efforts at the Max-Planck-Institut in Stuttgart Germany, Wesolowski et al. Appl. Phys. Lett. 71 (14), pp 1948-1950, Oct. 6, 1997, have produced nanodiamonds but only after soot is irradiated for 30 hour at temperatures of between 700 and 1100.degree. C. at high ion fluences of more than 10.sup.19 ions-cm.sup.-2.
Earlier research at the same institute, Banhart et al., Nature 382 pp 433-435 (1996) discloses a method for diamond production by irradiating carbon onions with high electron fluences of more than 10.sup.24 e.sup.-cm.sup.-2 at a sample temperature of 700.degree. C.
Explosive shock methods for nanodiamond formation are also known.
Nanometer-size diamonds are the detonation products of reactions described throughout the scientific literature, including "Diamonds in Detonation Soot," Nature Vol. 333, pp 440 (Jun. 2, 1988). Additional methods for producing and modifying nanodiamonds are disclosed in "Influence of the Molecular Structure of Explosives on the Rate of Formation, Yield, and Properties of Ultradisperse Diamond," Combustion, Explosion, and Shock Waves, Vol. 30, No. 2, pp 235-238 (Plenum Publishing Corp, New York, N.Y. 1994), which is a translation of Fizika Goreniya i Vzryva, Vol. 30, No. 2, pp. 102-106, March-April 1994. Diamonds ranging in size of from 2-20 nanometers are produced in methods described in "Synthesis of Ultradispersed Diamond in Detonation Waves" Combustion, Explosion, and Shock Waves, Vol 25, No. 3, pp 372-379, (Plenum Publishing Corp. New York, N.Y. 1994), which is a translation of Fizika Goreniya i Vzryva, Vol. 25, No. 3, pp 117-126, May-June, 1989.
Other sources and methods for obtaining nanodiamonds can be found in U.S. Pat. No. 5,709,577, issued on Jan. 20, 1998.
None of the prior art discussed supra provides a method for obtaining nanodiamonds under relatively mild conditions.
A need exists in the art for a process to produce nanometer sized diamonds at room temperature and at ambient pressures. The process should yield diamonds from a myriad of carbonaceous materials and in reasonably short periods of time. Furthermore, the process should isolate the product diamond from the carbonaceous starting material with a minimum of product loss and effort.